Within power conversion products, there is a need for high speed digital links that provide high isolation at a low cost. Typical digital links within power conversion products require a speed of 50-100 megabits per second. Isolation between the input and output of power conversion products is required in the range of 2,500-5,000 V. Existing solutions for providing a high speed digital isolation link have focused on the use of magnetic pulse couplers, magnetic resistive couplers, capacitive couplers and optical couplers.
Referring now to FIG. 1, there is illustrated the general block diagram of a system using a magnetic pulse coupler to isolate a digital link 102 between a driver 104 and a detector 106. The driver 104 resides upon one side of the digital link 102 and transmits information over the digital link 102 to the detector 106 residing on the other side of the digital link. Resting between the driver 104 and detector 106 is a pulse transformer 108. The pulse transformer 108 provides a electromagnetically coupled transformer between the driver 104 and detector 106. The pulse transformer 108 generates a pulse output in response to a provided input from the driver as illustrated in FIG. 2. The input from the driver 104 consists of the two pulses 202 and 204. Each pulse 202, 204 consists of a rising edge 206 and a falling edge 208. In response to a rising edge 206, the output of the pulse transformer 108 generates a positive pulse 210. The falling edge 208 of a pulse generates a negative pulse 212. The pulse transformer circuit illustrated with respect to FIGS. 1 and 2 suffers from a number of deficiencies. These include start-up where the detector 106 will not know at what point the input from the driver has begun, whether high or low until a first edge is detected. Additionally, should any error occur in the pulse output of the pulse transformer 108, the detector 106 would have a difficult time determining when to return to a proper state since there may be a long period of time between pulses.
Referring now to FIG. 3, there is illustrated an alternative prior art solution making use of a magneto resistive coupler. The magneto resistive coupler 302 consists of a resistor 304 and associated transformer 306. The resistor 304 has a resistance value that changes responsive to the magnetic flux about the resistor. The transformer detector 306 utilizes a wheatstone bridge to detect the magnetic flux of the resistor and determined transmitted data.
Another method of isolation between a driver 404 and a detector 406 is illustrated in FIG. 4. The driver 404 and the detector 406 are isolated on opposite sides of a digital link 402 by a capacitor 408. The capacitor 408 capacitively couples the driver 404 and detector 406 together to achieve a level of isolation. A problem with the use of capacitive coupling to isolate digital links is that capacitive coupling provides no common mode rejection.
An additional problem with some isolator designs involves the reception of RF interference from nearby transmitting GSM, DCS and CDMA cellular telephones. The problem is caused by the application printed circuit board acting as a dipole antennae at GHz frequencies. This results in large common mode signals being seen at the isolator at RF frequencies. Some manner for minimizing these large common mode signals at GHz frequencies would be highly desirable.
Thus, as compared to other isolation technologies, RF isolators offer advantages of smaller size, shorter propagation delays and higher data rates. When multiple communication channels are utilized, multiple RF isolators would be necessary in order to transmit information over multiple channels. However, the increase of RF isolators necessary to maintain a one-to-one correspondence between the RF isolators and the communication channels require the use of greater die areas upon a chip. Thus, some manner for limiting the number of RF isolators implemented within a multi channel communication device would be greatly beneficial.